Low temperature oxydehydrogenation of ethane to ethylene has become well known since the publication of "The Oxidative Dehydrogenation of Ethane over Catalyst Containing Mixed Oxide of Molybdenum and Vanadium" by E. M. Thorsteinson, T. P. Wilson, F. G. Young and P. H. Kasai, Journal of Catalysis 52, pp. 116-132 (1978). This article discloses mixed oxide catalysts containing molybdenum and vanadium together with another transition metal oxide (Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce). The catalyst are active at temperatures as low as 200.degree. C. for the oxydehydrogenation of ethane to ethylene.
The effectiveness of the oxydehydrogenation of ethane to ethylene is usually primarily determined by two parameters: conversion of ethane, and selectivity (efficiency) to ethylene. As used herein, these terms are defined as follows: ##EQU1## selectivity (efficiency) to ethylene= ##EQU2## wherein: []= relative moles of the component and the production of acetic acid is negligible. The terms in the art are sometimes calculated differently but the values calculated either way are substantially the same.
Under certain reaction conditions, substantial amounts of acetic acid can be formed as a co-product and the effectiveness of the reaction to ethylene and acetic acid is calculated by the following equations: ##EQU3## selectivity (efficiency) to ethylene and acetic acid= ##EQU4##
U.S. Pat. No. 4,250,346 discloses catalytic oxydehydrogenation of ethane to ethylene at temperatures less than 550.degree. C. in which the catalyst is a calcined composition comprising the elements Mo, X, and Y in the ratio EQU Mo.sub.a X.sub.b Y.sub.c
wherein:
X=Cr, Mn, Nb, Ta, Ti, V, and/or W PA1 Y=Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl, and/or U PA1 a=1 PA1 b=0.05 to 1.0 PA1 c=0 to 2 PA1 M=Bi, Te, Sb, Sn, and/or Cu PA1 N=Mo and/or W PA1 A=alkali, Tl, and/or Sm PA1 C=Ni, Co, Mn, Mg, Be, Ca, Si, Ba, Zn, Cd, and/or Hg PA1 D=Fe, Cr, Ce, and/or V PA1 E=P, As, B, Sb PA1 F=rare earth, Ti, Zr, Nb, Ta, Re, Ru, Ag, Au, Al, Ga, In, Si, Ge, Pb, Th, and/or U PA1 a=0 to 4 PA1 b=0 to 20 PA1 c=0.01 to 20 PA1 d=0 to 4 PA1 e=0 to 8 PA1 f=8 to 16 PA1 m=0.10 to 10 PA1 n=0.1 to 30, and PA1 x and y are numbers such that the valence requirements of the other elements for oxygen are satisfied; and the ratio q/p is 0.1 to 10. PA1 a=0.5 to 0.9 PA1 b=0.1 to 0.4 PA1 c=0.001 to 0.2 PA1 d=0.001 to 0.1.
The numerical values of a, b, and c represent the relative gram-atom ratios of the elements Mo, X, and Y, respectively, which are present in the catalyst composition. The elements Mo, X, and Y are present in the catalyst composition in combination with oxygen.
The patent discloses a wide variety of compositions; however, all of the examples of the patent which include antimony, examples 27, 28, and 41, disclosed very poor results. Example 27 had a catalyst having a composition V.sub.3 Sb.sub.12 Ce.sub.1 and resulted in no selectivity for the formation of ethylene. Example 28 had catalyst having a composition Sb.sub.5 V.sub.1 Nb.sub.1 Bi.sub.5 and had an initial activity at 525.degree. C. with a selectivity of only 26%. Example 41 had a catalyst having a composition of Mo.sub.16 V.sub.4 Sb.sub.2 which provided a conversion of 6% with a selectivity of 95% at 300.degree. C., and a conversion of 23% and a selectivity of 75% at 400.degree. C.
U.S. Pat. No. 4,339,355 discloses a catalytic oxide of molybdenum, vanadium, niobium, and a fourth metal which is Co, Cr, Cu, Fe, In, Mn and/or Y. The patent discloses that the catalyst is suitable for the vapor phase catalytic oxidation of unsaturated aliphatic aldehydes to the corresponding saturated aliphatic carboxylic acid.
U.S. Pat. No. 4,148,757 discloses catalysts of the oxidation and/or ammoxidation of olefins. The patent is particularly directed to a novel process for producing oxidation and/or ammoxidation catalysts and sets forth the following general formula for such catalyst: EQU [M.sub.m N.sub.n O.sub.x ]q [A.sub.a, C.sub.b, D.sub.c, E.sub.d, F.sub.e, N.sub.f, O.sub.y ]p
wherein:
None of the catalysts disclosed in U.S. Pat. No. 4,148,757 are disclosed as being suitable for the oxydehydrogenation of ethane to ethylene. Moreover, the suitability of the catalyst for olefins teaches away from the use of the catalysts for the oxydehydrogenation of ethane to ethylene because it would be expected that the ethylene would be oxygenated.